Everyone believes they know the hard line Google will not cross for shutting down products, and everyone eventually is wrong.
1: GM also has a reputation for getting a product just right and then killing it.
You have your mail, storage, office suite, photos, chat, etc, hosted by Google, they made it easy to host your domain there working with all those services, and all that vertically integration kept us comfortably in their warm embrace.
Now they're selling it because... why? Only theory that holds water is it doesn't make _enough_ money. Well sure it isn't a huge revenue source but it isn't losing money either, and the intangibles felt like they more than justified keeping it in-house.
Hopefully the inside story comes out, as I would be fascinated to hear their thought process.